five minute vactrols for the breadboard - and sheathed cable

[duck_arse]

that old parallel printer cable I'm always saying to cut-up for hookup wire, the one with 25 different colours, has an outer sheath with an inner dia of just about 5mm. your garden variety LDR's are also 5mm dia, and LED's also have a 5mm package. so throw the lot together, and in 5 minutes you've got a vactrol. now you can hot-swap them, or race them with your friends.

if you already know how to remove a sheath without destroying the underlying insulations, skip this next bit. I dunno if this is "the method", but it's how I've stripped sheathed power and audio cables for a very long time.

get your sharp knife and carefully snick a line around the sheath, maybe 50mm from the end. don't cut all the way through, as you'll wreck the inners - only cut through about half the sheath thickness.

put the knife down, pick up the cable, and bend it about the snick until you see a white stress-line in the underlying pvc. seen centre left is one such bent snick (complete with a bridging bit, needing further knife work), showing the stress line.



if your snick is deep enough, the insulation will split along that white line as you further stress the pvc by bending. if it doesn't split, just touch/rock the knife across the stress line as you bend, and it will split cleanly. centre right shows a split starting, and the underlying strands.

you will need to practice the method if you don't know it, but the results are as shown bottom above. if you are a very patient and dexterous type, you might keep the inner foil in place to use as a reflector/director, or as a grounded/ing shield for the ldr in noisy situations. to this end, pull one or two wires out through the cut to loosen the bundle, as seen upper below, so as not to pull the shield as well. (I tried a few times, but mostly the foil will bunch and block the internal sightlines. pull the foil out and turf it.)

the end result should look about like the piece show below lower. the next step is to cut the long length to about 12mm lengths, shorter or longer to your ldr/led separations preference. the only way to do this neatly is to shove something inside for support. a 4.5mm drill would be about best, a screwdriver if that's all to hand. slice through the pvc, rotate, slice again until the end falls off. you can trim ragged edges, or chuck that bit and do another.



so's I know which type ldr I'm using, I slip a bit of (general purpose sized) hook-up wire insulation over the legs, colour coded to some part of the particular part number (shown below are GL5516 and 5539). poke your darning-needle-stuck-in-a-handle tool up the insulation to stretch it a little, and use 2 short lengths instead of a single long-enough length, it will be easier. the legs will now be insulated and stiffer.

same goes for the waterclear leds, colour code the kathode leg, for example, and you'll know what colour and which way every time. clip the led leads shortish. the ldr needs some hooky bending, as shown. use your pliers to grip one of the ldr's legs right up under the head to insert it into the sheath/tube/housing, it will be easier than trying to finger hold them. poke it in carefully and check it sits square, spaced from the led lens as you see fit.



now jamb the led in the other end, with its legs aligned with the ldr's - the led's flange will positive-stop it. splay the ldr legs a little, and it's done. you might like to make a little (white, as reflector) cardboard hat, to block the desklamp light as well. I find either of the popular Tardis shapes effective, or you can use a 35mm film can.

and look, here's one in action against the alternative method, on a breadboarded vibe.

[robthequiet]

Nice tutorial, DA. I probably have a century's supply of coax and ethernet to harvest, but never thought to match the actual diameter of the ldr. Since I'm pathological I would probably add a drop of hot glue to the ends. Cool.

[duck_arse]

ahh, rob, the original title was "5 minute vactrols - no heat, no glue", but I realised the mess could be made of the cable with a sharp blade, so included all that cutting stuff. no glue - they are only epherema for the breadboarding.

I now wonder if the cable de-sheathing method shown is the one everyone uses or not ..... anyone?

[midwayfair]

You clever mother quacker.

[GibsonGM]

Very nice, Duck!   I cut insulation that way, yes.  Some things are just far to fat for any common wire strippers to handle.

I would definitely try to keep the vactrols for permanent use - good idea!

[Kipper4]

Thanks Duck
I've been making my space saving vactrols like that for a while now but with heatshrink, NSL32 style.
Thanks for the tutorial. Now where did i put that computer printer cable i saved.
Shed? Loft? Junk cupboard? Junk room? Man drawer? I'll leave it tonight. meh.

[robthequiet]

I now wonder if the cable de-sheathing method shown is the one everyone uses or not ..... anyone?

I had a handy dandy professional coax stripper which is more trouble than it's worth. Usually use big wire cutters to score the outside and the pretty much as you.